Castor



FIG. 1 is a top perspective view of a castor showing my new design;

FIG. 2 is a left side elevational view thereof, the right side being identical thereto;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a front elevational view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom plan view thereof. 

The ornamental design for a castor, as shown and described. 